In digital audio equipment or the like, sampling rates are used that are different for the digital signals of different systems. Accordingly, sampling rate conversion is needed to exchange data between different systems. A device that converts a sampling rate while maintaining the identity of a waveform signal such as an audio signal is known as a sampling rate converter.
In a sampling rate converter, output data is calculated by interpolation. Optimal characteristics of an LPF used for the interpolation differ depending upon the sampling rate ratio (sampling frequency ratio) of the input digital signal sampling rate to the output digital signal sampling rate. Accordingly, it has been necessary, in order to provide a sampling rate converter capable of coping with a plurality of sampling rate ratios, to prepare a plurality of LPFs in the converter and to select an optimal LPF in accordance with the sampling rate ratio of concern.
Although it is designed to deal with a plurality of sampling rate ratios, a conventional sampling rate converter is actually adapted for conversion between only specific sampling rates and required to be capable of coping with only predetermined specific sampling rate ratios. Accordingly, it is only necessary to predetermine an optimal LPF for each sampling rate ratio.
However, a conventional sampling rate converter cannot cope with applications in which sampling rate ratios to be dealt with are not limited to specific ratios. For such applications, a novel device is needed for selecting an optimal LPF.